154 CRUSTACEA EUCARIDA DECAPODA CHAP. 



Tribe 1. Nephropsidea. 



This tribe includes the Lobsters and Crayfishes, animals well 

 known from their serviceableness to man. There are three 

 families, which will be treated separately. 



Fam. 1. Nephropsidae. The podobranchs are not united 

 with the epipodites, and the last thoracic segment is fixed and 

 fused to the carapace. The chelae are generally asymmetrical. 

 The most important Lobsters are the European and the American 

 species Ho mar us vulgar is ( = Astar.us gammarus} and H. ameri- 

 canus respectively ; these animals engage a large number of people 

 in the fisheries. It is estimated that in America about 150,000 

 are spent every year on Lobsters. 



The genus NepJirops contains the small Norwegian lobster 

 and other forms. 



Herrick l gives some interesting particulars with regard to 

 the life-history of the American species. The largest recorded 

 specimen weighed about twenty-five pounds, and measured twenty 

 inches from rostrum to tail ; similar European specimens have 

 been recorded, but, on the average, they are not so large as the 

 American forms. 



The Lobster, like all Crustacea, undergoes a series of moults 

 as the result of increase in size, shedding the whole of the 

 external integument in one piece. This is accomplished by 

 a split taking place on the dorsal surface at the junction of 

 thorax and abdomen ; through the slit so formed the Lobster 

 retracts first his thorax with all the limbs, and then his abdomen. 

 When first issuing from the old shell the animal's integument is 

 soft and pulpy, but the increase in size of the body is already 

 manifest ; this increase per moult, which is approximately the 

 same in young and adult animals, varies from 13 to 15 per cent of 

 the animal's length. According to this computation, a Lobster 

 2 inches long has moulted fourteen times, 5 inches twenty times, 

 and 10 inches twenty-five times, and it maybe roughly estimated 

 that a 10-inch Lobster is four years old. Young Lobsters 

 probably moult twice a year, and so do adult males, but females 

 only moult once a year soon after the young are hatched out. 



The process of moulting or ecdysis is an exceedingly 



1 Bull. U.S. Fish Commission, xv., 1895. 



